The invention relates to an improved method of preparing cast sulfur-asphalt compositions wherein mixtures of sulfur and asphalt are mixed and/or heated at elevated temperatures to facilitate casting. More particularly, this invention is directed to a means for substantially suppressing the emission of hydrogen sulfide in the casting process described and to sulfur asphalt compositions containing agents which minimize hydrogen sulfide evolution at the high temperatures required for casting.
As described in British Pat. No. 1,363,706, mixtures of sulfur, asphalt and mineral aggregate can be successfully cast into formed compositions such as pavements and construction articles, provided the sulfur and asphalt are present at a weight ratio of at least 1:1 sulfur to asphalt and the casting is carried out without the application of densification pressures. According to this patent teaching, the mixture should not be heated above 175.degree.C in the casting process since above this temperature a chemical reaction between sulfur and asphalt takes place accompanied with emission of hydrogen sulfide. Preferably, the mixing temperature is 150.degree.C or lower.
It has now been observed that when working at such a temperature below, but approaching 175.degree.C, and casting the sulfur-asphalt composition into a formed article, e.g., spreading the hot mix on the road, measurable quantities of hydrogen sulfide are evolved. Although the quantity of hydrogen sulfide amounts only to some parts per million, environmental considerations may make it desirable to reduce these hydrogen sulfide concentrations further. The instant invention provides a means or accomplishing this environmentally desirable objective.